The American Society of Clinical Oncology (ASCO) recently updated its guidelines for breast cancer, which state that patients with breast cancer who have a negative sentinel lymph node (SLN) biopsy may not undergo axillary lymph node dissection (ALND). The guidelines also apply to most breast cancer patients with only 1-2 SLN metastases who are scheduled for breast-conserving surgery or whole-breast radiation therapy. The guidelines are a significant departure from previous guidelines, which recommended that all patients with SLN-infiltrating breast cancer should undergo ALND, and the results of a study in the JCO journal, which also suggested that patients with SLN metastases who choose to undergo mastectomy should undergo ALND. Gary Lyman, MD, of the Fred Hutchinson Cancer Research Center and chair of the expert panel that developed the guidelines, said, “The guidelines were developed based on the results of a recent clinical trial that showed that SLN biopsy alone had the same prognosis and few complications as patients who also underwent ALND. “ Whether or not ALND is performed has little impact on treatment options or improving patient prognosis; rather, patients who do not undergo ALND tolerate it better. If a patient is planning to have a mastectomy and is not going to have radiation therapy, ALND is still indicated. No ALND greatly reduces lymph node edema, which can cause severe arm weakness, numbness and shoulder pain. This is the first update to the ASCO guidelines since they were published in 2005. At this point, the guidelines include only a single randomized clinical trial that showed no axillary metastases in patients without lymph node invasion and who did not undergo ALND. Short-term survival rates were similar for patients who underwent SLN biopsy and those who underwent ALND. The guideline update also includes high-quality clinical studies, such as the American Society of Surgical Oncology’s Z0011 study, whose results also support that patients with only 1-2 SLN metastases should not undergo ALND. Lyman says, “As with many other trials, if performing ALND does not improve patient prognosis and clinical decision making, then that’s when we should think more about its potential harms.” Researchers have done a good job of defining which patients should not undergo ALND, and the guidelines have been developed to provide patients and oncologists with the latest evidence-based medical evidence. SLN biopsies are indicated for breast cancer patients with multicentric tumors, ductal carcinoma in situ with mastectomy, prior mastectomy or axillary lymph node dissection, and preoperative systemic or adjuvant chemotherapy. The guidelines also specify when SLN biopsy is contraindicated: large or locally advanced invasive breast cancer; inflammatory breast cancer; ductal carcinoma in situ in preparation for breast-conserving surgery; and breast cancer during pregnancy. More research is needed on when SLN biopsy can be used instead of ALND. In clinical work, specific patients should also be treated on a case-by-case basis, which is the essence of individualized medicine.